Variable and constant names

Variable and constant names must begin with a letter. They can contain the letters A to Z and a to z, the underscore symbol (_), and the digits 0 to 9. Variable and constant names must begin with a letter, be no longer than 40 characters, and cannot be reserved words.

For a table of reserved words, refer to Functions, statements and reserved words - Quick reference.

Note: One exception to this rule is that object member names and property names can be reserved words.